The invention relates to power supplies in general and more particularly, it relates to a digital controller which prevents the build-up of magnetic current in a pulse-width modulated driven transformer.
Traditionally, off-line analog switching regulators designs have resulted in a high component count which adversely affects the reliability, package size and overall cost. Analog feedback control systems experience both short and long term stability problems because of component drift. Secondly, each output voltage to be regulated requires a dedicated analog control system. This means that power systems which produce multiple, independent, regulated output voltages must have an independent analog controller for each voltage, since many contemporary applications require three to five independent voltages, while duplicated analog circuitry contributes significantly to the cost of their power systems. Analog systems are not flexible enough to adapt to widely varying applications.
An ideal feedback control system would be one that could incorporate the advantages of proportional and derivative control for multiple, independent, regulated output voltages at low cost in a simple implementation that is relatively independent of component drift and would adapt to different needs. In those power systems which utilize a push-pull drive arrangement, it is well known that differences in the power-on and power-off time periods of the power switching devices will cause the power transformer to gradually build up a magnetizing current resulting in the saturation of the transformer. Prior analog switching regulators in trying to solve this problem have A.C. coupled the transformer drive signals with expensive poly-carbonate or polystyrene capacitors because of their low loss characteristics in the presence of the high frequency ripple currents. It is therefore an object of this invention to provide a system controller for a power supply which is digital in construction enabling the controller to be incorporated into a single LSI circuit chip and which provides effective current balance protection. It is a further object of this invention to provide a digital controller for a power supply which prevents the build-up of magnetizing current in the transformer and utilizes pulse width modulation control for the power supply regulation. A further object of this invention is to provide a digital constructed power supply controller providing current balance protection which is simple in construction and therefore low in cost.